uniform vec3 iResolution;
uniform float iTime;
uniform vec2 iMouse;

#define time iTime

mat2 mm2(in float a){float c = cos(a), s = sin(a);return mat2(c,s,-s,c);}
mat2 m2 = mat2(0.95534, 0.29552, -0.29552, 0.95534);
float tri(in float x){return clamp(abs(fract(x)-.5),0.01,0.49);}
vec2 tri2(in vec2 p){return vec2(tri(p.x)+tri(p.y),tri(p.y+tri(p.x)));}

float triNoise2d(in vec2 p, float spd)
{
  float z=1.8;
  float z2=2.5;
  float rz = 0.;
  p *= mm2(p.x*0.06);
  vec2 bp = p;
  for (float i=0.; i<5.; i++ )
  {
    vec2 dg = tri2(bp*1.85)*.75;
    dg *= mm2(time*spd);
    p -= dg/z2;

    bp *= 1.3;
    z2 *= .45;
    z *= .42;
    p *= 1.21 + (rz-1.0)*.02;
    
    rz += tri(p.x+tri(p.y))*z;
    p*= -m2;
  }
  return clamp(1./pow(rz*29., 1.3),0.,.55);
}

float hash21(in vec2 n){ return fract(sin(dot(n, vec2(12.9898, 4.1414))) * 43758.5453); }
vec4 aurora(vec3 ro, vec3 rd)
{
  vec4 col = vec4(0);
  vec4 avgCol = vec4(0);
  
  for(float i=0.;i<50.;i++)
  {
    float of = 0.006*hash21(gl_FragCoord.xy)*smoothstep(0.,15., i);
    float pt = ((.8+pow(i,1.4)*.002)-ro.y)/(rd.y*2.+0.4);
    pt -= of;
    vec3 bpos = ro + pt*rd;
    vec2 p = bpos.zx;
    float rzt = triNoise2d(p, 0.06);
    vec4 col2 = vec4(0,0,0, rzt);
    col2.rgb = (sin(1.-vec3(2.15,-.5, 1.2)+i*0.043)*0.5+0.5)*rzt;
    avgCol =  mix(avgCol, col2, .5);
    col += avgCol*exp2(-i*0.065 - 2.5)*smoothstep(0.,5., i);
  }
  col *= (clamp(rd.y*15.+.4,0.,1.));
  return col*1.8;
}

vec3 nmzHash33(vec3 q)
{
  uvec3 p = uvec3(ivec3(q));
  p = p*uvec3(374761393U, 1103515245U, 668265263U) + p.zxy + p.yzx;
  p = p.yzx*(p.zxy^(p >> 3U));
  return vec3(p^(p >> 16U))*(1.0/vec3(0xffffffffU));
}

vec3 stars(in vec3 p)
{
  vec3 c = vec3(0.);
  float res = iResolution.x*1.;
  
  for (float i=0.;i<4.;i++)
  {
    vec3 q = fract(p*(.15*res))-0.5;
    vec3 id = floor(p*(.15*res));
    vec2 rn = nmzHash33(id).xy;
    float c2 = 1.-smoothstep(0.,.6,length(q));
    c2 *= step(rn.x,.0005+i*i*0.001);
    c += c2*(mix(vec3(1.0,0.49,0.1),vec3(0.75,0.9,1.),rn.y)*0.1+0.9);
    p *= 1.3;
  }
  return c*c*.8;
}

vec3 bg(in vec3 rd)
{
  float sd = dot(normalize(vec3(-0.5, -0.6, 0.9)), rd)*0.5+0.5;
  sd = pow(sd, 5.);
  vec3 col = mix(vec3(0.05,0.1,0.2), vec3(0.1,0.05,0.2), sd);
  return col*.63;
}

void main()
{
  vec2 q = gl_FragCoord.xy / iResolution.xy;
  vec2 p = q - 0.5;
  p.x*=iResolution.x/iResolution.y;
  
  vec3 ro = vec3(0,0,-6.7);
  vec3 rd = normalize(vec3(p,1.3));
  vec2 mo = iMouse.xy / iResolution.xy-.5;
  mo = (mo==vec2(-.5))?mo=vec2(-0.1,0.1):mo;
  mo.x *= iResolution.x/iResolution.y;
  rd.yz *= mm2(mo.y);
  rd.xz *= mm2(mo.x + sin(time*0.05)*0.2);
  
  vec3 col = vec3(0.);
  vec3 brd = rd;
  float fade = smoothstep(0.,0.01,abs(brd.y))*0.1+0.9;
  
  col = bg(rd)*fade;
  
  if (rd.y > 0.){
    vec4 aur = smoothstep(0.,1.5,aurora(ro,rd))*fade;
    col += stars(rd);
    col = col*(1.-aur.a) + aur.rgb;
  }
  else //Reflections
  {
    rd.y = abs(rd.y);
    col = bg(rd)*fade*0.6;
    vec4 aur = smoothstep(0.0,2.5,aurora(ro,rd));
    col += stars(rd)*0.1;
    col = col*(1.-aur.a) + aur.rgb;
    vec3 pos = ro + ((0.5-ro.y)/rd.y)*rd;
    float nz2 = triNoise2d(pos.xz*vec2(.5,.7), 0.);
    col += mix(vec3(0.2,0.25,0.5)*0.08,vec3(0.3,0.3,0.5)*0.7, nz2*0.4);
  }
  
  gl_FragColor = vec4(col, 1.);
}